Electronic pens are known, which have sensors and electronic devices for digitally recording what is being written by means of the pen. Different kinds of sensors can be mounted in the pen in order to determine its position, for instance acceleration sensors as described in U.S. Pat. No. 5,434,371 and U.S. Pat. No. 6,130,666, optical sensors as described in U.S. Pat. Nos. 5,294,792, 5,852,434 and WO 00/73983, pressure sensors as described in U.S. Pat. No. 6,104,388, or mechanical sensors as described in U.S. Pat. No. 5,294,792 and U.S. Pat. No. 6,130,666. In other types of electronic pens, use is made of triangulation of signals (for instance light, sound or IR radiation) for position determination, which is described in U.S. Pat. No. 5,012,049.
The above-described and other inner components of the pen may necessitate service, exchange, calibration and other measures, and therefore the pen body is most suitably designed so as to allow access to the components. For this purpose and to facilitate the assembly of the pen, the pen body comprises a casing which accommodates the components that are to be accessible and consists of casing parts which are joined to be separable. The separable joining is implemented with e.g. screws. A problem in the context is that consequently the casing can also can be opened, for instance, by a user who does not have the necessary knowledge of handling the components in the interior of the pen. It is difficult, when the pen is handed in for service, to determine whether the deficiencies that may have arisen in the inner components of the pen are caused by the pen being opened by a person who is not authorized to perform service of the pen, for which reason a previously granted warranty or guarantee should not be valid.